Biomedical subjects

K Stuart

Publications and source records attributed to K Stuart.

At least 109 records · Page 6Linked to original sources

PubMed1988

Characterization of cytochrome c oxidase III transcripts that are edited only in the 3' region.

The cytochrome c oxidase subunit III (COIII) transcript of T. brucei is extensively edited by the addition and deletion of uridines. We have identified partially edited COIII RNAs; they have unedited 5' and edited 3' regions. Transcripts with edited 5' but unedited 3' regions were not detected. The partially edited RNAs may be editing intermediates. The junctions of unedited and edited sequences in cDNAs differ from both the DNA and fully edited mRNA sequences over a multinucleotide region. The partially edited RNAs could arise from several processes, but it seems likely that editing proceeds in the 3' to 5' direction.

Animals↗

PubMed1988

Editing of kinetoplastid mitochondrial mRNAs by uridine addition and deletion generates conserved amino acid sequences and AUG initiation codons.

RNA editing is a novel type of mRNA processing in the kinetoplastid mitochondrion that involves the co- or posttranscriptional addition of uridine residues within transcripts. The result is an mRNA nucleotide sequence which differs from that of the corresponding gene. We have found that RNA editing may also occur through the deletion of genome-encoded uridines from the RNA sequence. Uridine additions and deletions in the 5' ends of the COIII, MURF2, and MURF3 transcripts create new N-terminal amino acid sequences that are conserved between species, and new AUG initiation codons in several cases. These results suggest that the creation of new amino acid sequences and methionine initiation codons may be important functions of RNA editing in the kinetoplastid mitochondrion.

Amino Acid Sequence↗

PubMed1988

Extensive editing of the cytochrome c oxidase III transcript in Trypanosoma brucei.

The gene for cytochrome oxidase subunit III (COIII) is not detected in T. brucei by nucleotide sequence analysis or by cross-hybridization studies. We have identified the COIII transcript in the T. brucei mitochondrion by RNA and cDNA sequencing. Its nucleotide and predicted amino acid sequences are very similar to those from the COIII genes in related species. A mitochondrial DNA sequence that matches the COIII transcript, except for the absence of numerous thymidines, is located upstream of the apocytochrome b gene, the position of the COIII gene in related species. We conclude that this sequence is the COIII gene and that over 50% of the T. brucei COIII transcript sequence is created by RNA editing.

Amino Acid Sequence↗

PubMed1988

Creation of AUG initiation codons by addition of uridines within cytochrome b transcripts of kinetoplastids.

The cytochrome b gene of Trypanosoma brucei has an ATG codon near its 5' end but the cytochrome b genes of the related kinetoplastids Leishmania tarentolae and Crithidia fasciculata lack an ATG. Recent results have shown that 34 uridines that are not encoded in the genome are added within the 5' end of T. brucei cytochrome b transcripts during or after transcription. These additions create an AUG in the transcript that is 20 amino acids upstream of the AUG predicted from the genomic sequence. We report here that the cytochrome b transcripts of L. tarentolae and C. fasciculata also contain added uridines within their 5' ends. The additions occur in similar numbers and positions and an in frame AUG is created at a similar site in all three species. These data strongly suggest that the created AUG functions as the initiation codon for cytochrome b in these species. Since some other kinetoplastid mitochondrial genes also lack conventional initiation codons, creation of initiation codons may be an important function of uridine addition.

Amino Acid Sequence↗

PubMed1988

LR1: a candidate RNA virus of Leishmania.

Although viruses are important biological agents and useful molecular tools, little is known about the viruses of parasites. We report here the discovery of a candidate for an RNA virus in a kinetoplastid parasite. This potential virus, which we term LR1, is present in the promastigote form of the human pathogen Leishmania braziliensis guyanensis CUMC1-1A but not in 11 other stocks of Leishmania that were examined nor in Trypanosoma brucei. The candidate viral RNA has a size of approximately 6000 nucleotides, is single-stranded, and is largely, if not exclusively, located in the cytoplasm. No homologous LR1 sequences are detected in genomic DNA. The candidate viral RNA is associated with a spherical particle 32 nm in diameter that has a sedimentation coefficient of approximately 130 S. There is as yet no evident effect of this potential virus on parasite physiology or the disease caused by the parasite.

Animals↗

PubMed1988

Developmental aspects of uridine addition within mitochondrial transcripts of Trypanosoma brucei.

The mitochondrial respiratory system is absent in slender bloodstream forms of Trypanosoma brucei, incomplete in stumpy bloodstream forms, and complete in procyclic (insect) forms. The steady-state abundance of transcripts of some mitochondrially encoded components of the respiratory system correlates with its differential expression in different life cycle stages. Recently, it was reported that uridines which are not encoded in the genome are added to cytochrome b and cytochrome oxidase II transcripts. We now report that the (U)+ transcripts of both genes are found in procyclic forms and to some degree in stumpy forms but are absent in slender forms. The uridine additions to cytochrome oxidase II correct a frameshift in the gene and presumably allow production of a full-length protein, whereas those added to cytochrome b create an in-frame AUG which extends the N terminus of the predicted protein by 20 amino acids. The stage specificity of uridine additions to these transcripts thus reflects the life cycle stage during which the protein products would be used. Transcripts of MURF2, a gene of unknown function, have additional uridines in both slender and procyclic forms which create two in-frame AUGs. MURF2 transcripts additionally differ from the DNA sequence in ways which cannot be explained by uridine addition alone, implying that other processes alter these transcripts.

Animals↗

PubMed1988

Prognosis of lean and fat hypertensives.

A population sample of 1,645 men aged 40-59 at entry examination has been followed up for 25 years. When hypertensives (160 and/or 95 mm Hg or more; n = 432) were divided into fat and lean on the basis of body mass index (cut off at 24.9), the latter group showed a nonsignificant higher risk of dying during the subsequent 25 years (relative risk = 1.15). Univariate and multivariate analyses suggest that among lean people there is an excess of smokers partly explaining the excess risk of lean hypertensives. Both univariate and multivariate analyses also proved that the relationship of fatness-leanness indicators to total mortality is U-shaped and applies to hypertensives as well as to nonhypertensives, and to the whole population. Evidence has been given that changing the definition of fatness-leanness (cutoff of body mass index of 27.9) the relative risk of lean versus fat hypertensives may reverse (0.93). This suggests that a large part of the problem is artificial and should not be tackled without considering the parabolic relationships of indicators of obesity to mortality.

Adult↗

PubMed1987

Developmentally regulated addition of nucleotides within apocytochrome b transcripts in Trypanosoma brucei.

Production of the mitochondrial respiratory system and expression of mitochondrial genes are developmentally regulated in T. brucei. We have found three classes of apocytochrome b (CYb) transcripts. Two of these contain U's within their 5' sequence that are not found in the CYb gene. They occur in procyclic forms, which have a complete mitochondrial respiratory system, but are absent in bloodstream forms, which lack this respiratory system. The third transcript has the sequence predicted from the genomic sequence and is present in both life cycle stages. These findings suggest that there is developmentally regulated posttranscriptional addition of U's to CYb transcripts. This process may contribute to the developmentally regulated production of the mitochondrial respiratory system.

Animals↗

PubMed1987

Comparison of the maxicircle (mitochondrial) genomes of Leishmania tarentolae and Trypanosoma brucei at the level of nucleotide sequence.

The entire 16.7-kilobase (kb) transcribed region of the Leishmania tarentolae maxicircle was compared to the entire 15-kb transcribed region of the Trypanosoma brucei maxicircle at the nucleotide sequence level by dot matrix analysis and by alignments of individual genes. The L. tarentolae NADH dehydrogenase subunit 1 (ND1) gene was identified in a newly obtained 2.9-kb sequence. All but two regions which flank the cytochrome b gene are highly conserved in both species. One 3.1-kb region in L. tarentolae that contains the cytochrome oxidase subunit III (COIII) gene and several open reading frames corresponds to a 2-kb sequence in T. brucei with limited sequence homology that lacks the COIII gene. Another 0.6-kb region that comprises an unidentified open reading frame (open reading frame 12) in L. tarentolae is substituted by a nonhomologous 0.4-kb open reading frame in T. brucei. A short intergenic region between the ND1 gene and the maxicircle unidentified reading frame 1 gene shows limited sequence homology, and the regions between the ND4 and ND5 genes and between the COI and ND4 genes are not conserved. All of the intergenic regions share G + C richness and a similar pattern of G versus C strand bias. 1.8 kb of the L. tarentolae divergent region (DV) and around 3 kb of the T. brucei DV were also obtained. The T. brucei DV sequences were not homologous to the L. tarentolae DV sequence but were organized in a similar fashion with tandem repeats of varying complexity.

Animals↗

PubMed1987

Variation of G-rich mitochondrial transcripts among stocks of Trypanosoma brucei.

We have compared maxicircle transcripts from eight stocks of subspecies of Trypanosoma brucei. Transcripts from the rRNA and protein genes have a constant size among stocks and exhibit only minor variation in abundance. In contrast, four of the G+C rich sequences encode multiple transcripts that very markedly in size or abundance. Maxicircle nucleotide sequence comparison of three stocks shows very limited sequence divergence suggesting that sequence divergence may not explain the transcript variability. These results suggest that the G-rich transcripts do not encode proteins and that their variability among stocks may result from posttranscriptional processing events.

Animals↗

PubMed1986

Development of the nephrotic syndrome in a patient with prostatic carcinoma.

Various malignancies have been associated with the nephrotic syndrome. The nephrotic syndrome developed in a 66-year-old man with metastatic prostatic carcinoma. Renal biopsy revealed membranous glomerulonephritis. This may be the first reported case of a clear association of prostatic carcinoma with biopsy-proved membranous glomerulonephritis.

Aged↗

PubMed1986

Conservation of kinetoplastid minicircle characteristics without nucleotide sequence conservation.

The nucleotide sequence and restriction fragment electrophoretic mobility of four minicircles from the kinetoplast DNA of Trypanosoma brucei were determined. Each minicircle possesses an approximately 130 base pair conserved sequence which occurs in other African trypanosome minicircles and contains a 13 base pair sequence that is conserved among kinetoplastid genera [Kidane et al. (1984) Gene 27, 265-277]. A sequence located adjacent to the conserved sequence conserves purine versus pyrimidine strand bias, but not nucleotide sequence, and contains periodic oligo(dA) tracts. Minicircle fragments containing the conserved sequence and adjacent segment exhibited anomalous electrophoretic mobility in polyacrylamide gels. The position of the oligo(dA) tracts in the fragments appears to influence this anomalous mobility. The presence of conserved features independent of conserved nucleotide sequence and the lack of conserved open reading frames among these minicircles suggests that minicircles may have a function other than encoding protein.

Animals↗

PubMed1986

Sequence organization in African trypanosome minicircles is defined by 18 base pair inverted repeats.

We have found that minicircles of African trypanosomes contain 18 base pair sequences that occur as 3 or 4 pairs of imperfect inverted repeats. The 18 base pair sequence is polar; one half is almost perfectly conserved, while the other half has a more variable sequence. The distribution of the 18 base pair sequences in minicircles defines two classes of sequences ('A' and 'B' segments) that have distinct characteristics. 'A' segments vary considerably in length and contain about 10% more G+C than 'B' segments which are all about 100 base pairs long. The 18 base pair sequences are absent from minicircles of other kinetoplastids. Thus, 'B' segments along with their terminal 18 base pair sequences superficially resemble insertion sequences. Minicircles of African trypanosomes therefore conserve their organization but have only limited nucleotide sequence homology.

Animals↗

PubMed1986

Differential mitochondrial gene expression between slender and stumpy bloodforms of Trypanosoma brucei.

Bloodforms of Trypanosoma brucei lack complete cytochrome and Krebs cycle systems but a fully functional mitochondrial respiratory system is elaborated upon differentiation to procyclics. We previously found differential expression of some mitochondrial genes, at the level of transcript abundance, between these two life cycle stages. We report here that mitochondrial genes are also differentially expressed between the two morphological types of bloodforms. Some transcripts that are more abundant in procyclics than slender bloodforms are intermediate in abundance in stumpy bloodforms. Most major mitochondrial transcripts are more abundant in stumpy than slender bloodform RNA; some are also more abundant than in procyclic RNA. Transcripts from protein coding genes are increased in abundance to varying degrees. Treatment with difluoromethylornithine, which induces a stumpy morphology, produces transcript abundance patterns similar to those in naturally occurring stumpy bloodforms. Stumpy bloodforms also have a decrease in tubulin transcript abundance, consistent with their nondividing character and smaller flagellum. These studies suggest that molecular events associated with mitochondrial development during the differentiation from bloodforms to procyclics can be initiated in the bloodstream, and that maxicircle transcript abundances are individually modulated during the life cycle.

Animals↗

PubMed1986

Molecular karyotype of species and subspecies of Leishmania.

The DNA karyotypes of three species and several subspecies of New World Leishmania were found to be distinct. The karyotypes were more similar among closely related isolates than among more distantly related groups. Two classes of chromosomal DNA differences were detected among stocks; +/- 50 kb size differences among DNAs, some of which were shown to contain homologous sequences, and DNAs having no obvious corresponding chromosomal DNA in other isolates. A total of 14-24 chromosomal DNA bands were resolved, depending on the isolate, but densitometric analyses suggest that these isolates contain 26-33 distinct DNA molecules. These molecules total about 2.5 X 10(7) bp, a substantial fraction of the genomic DNA. The chromosomal DNA locations of gene sequences homologous to alpha- and beta-tubulin, ribosomal RNA, thymidylate synthetase-dihydrofolate reductase, and the H-region sequence were determined. The homologous sequences were located on chromosomal DNAs of similar, but not identical sizes among different stocks. We also found species- and some subspecies-specific beta-tubulin chromosomal loci. We conclude that the DNA karyotype is useful for stock identification, taxonomy, and gene localization in Leishmania. Its potential for identifying the species and subspecies in natural infections appears less useful unless applied in conjunction with specific hybridization probes.

Animals↗

PubMed1985

Apocytochrome b and other mitochondrial DNA sequences are differentially expressed during the life cycle of Trypanosoma brucei.

Cytochromes and Krebs cycle enzymes are not detected in bloodstream forms of Trypanosoma brucei but are present in procyclic forms. We have analyzed transcription of mitochondrial sequences which contain the apocytochrome b gene and several other open reading frames (ORFs). Multiple transcripts map to individual DNA sequences located on both DNA strands. Larger low abundance transcripts map to multiple ORFs and may be precursor RNAs. Small abundant transcripts map to G + C rich sequences that do not have obvious protein coding functions. The larger of two presumptive apocytochrome b transcripts is strikingly more abundant in procyclic than bloodstream forms and other mitochondrial transcripts are also differentially abundant between these two forms. In addition, many mitochondrial transcripts appear to be differentially polyadenylated between bloodstream and procyclic forms. We suggest that the mechanisms which regulate the production of the mitochondrial respiratory system in T. brucei involve differential expression of mitochondrial genes.

Animals↗

PubMed1985

(TAA)n within sequences flanking several intrachromosomal variant surface glycoprotein genes in Trypanosoma brucei.

In Trypanosoma brucei telomeric copies of intrachromosomal variant surface glycoprotein (VSG) genes are produced through a gene conversion mechanism and are expressed if the telomere is or becomes transcriptionally activated. We have analyzed a sequence that occurs 1 to 1.5 kb 5' to several intrachromosomal VSG genes. This flanking sequence has three distinct sections: a 5' section containing 5 to 116 TAA or TAA-like tandem repeats; a moderately conserved sequence with an alternating GT characteristic; and a highly conserved 3' sequence that is largely alternating TA. Restriction mapping data and the location of this sequence suggest that it occurs at or near the 5' gene conversion boundary. This sequence, however, is not 5' to all VSG genes. These data suggest that this flanking sequence alone is not sufficient for VSG gene expression but that it may function in gene conversion for many, but not all, VSG genes.

Animals↗

PubMed1985

Preferential activation of telomeric variant surface glycoprotein genes in Trypanosoma brucei.

During an infection, Trypanosoma brucei expresses diverse variant surface glycoprotein (VSG) genes in a quasi-sequential order. Numerous VSG genes have intrachromosomal locations but many are located adjacent to telomeres. We have tested whether telomeric VSG genes are preferentially activated compared to intrachromosomal VSG genes during an antigenic switch. The frequency with which the IsTat 11 VSG gene is expressed in first relapse populations has been compared for variant antigenic types (VATs) A3 and A11. These VATs express the same A VSG gene from the same chromosome but VAT A11 contains an inactive telomeric 11 VSG gene which is absent in VAT A3. The 11 gene is activated at a much higher frequency in first relapse populations from VAT A11 than from VAT A3. A resultant VAT 11 clone was examined in detail and shown to have reactivated the telomeric 11 VSG gene. These results suggest that a telomeric location can result in a greater frequency of activation of a VSG gene. This preferential activation may explain, in part, the order of expression of VSG genes.

Animals↗